Provided are an apparatus for preparing a cathode active material precursor for lithium secondary batteries including a cylindrical outer chamber, an inner cylinder that has the same central axis as the outer chamber and is mounted to rotatably move along the central axis, an electric motor to transfer power to rotate the inner cylinder, a reactant inlet disposed on the outer chamber, to add reactants to a space between the outer chamber and the inner cylinder, and an outlet disposed in the outer chamber, to obtain reaction products after reaction in the space between the outer chamber and the inner cylinder, and a method for preparing a cathode active material precursor for lithium secondary batteries using the apparatus.